Hyper Extended is a constructed format composed of the black bordered sets from Fallen Empires to Scourge, including the Portal sets One and Second Age and the following promos.
All ante cards are banned.
Hyper Extended features a restricted list (Visual View):
Academy Rector Ancient Tomb Brainstorm Burning Wish Demonic Consultation Earthcraft Enlightened Tutor Frantic Search Goblin Recruiter Memory Jar Mind's Desire Mystical Tutor Necropotence Tinker Tolarian Academy Vampiric Tutor Windfall Yawgmoth's Bargain Yawgmoth's Will
No white bordered cards are allowed. No new frame or time shifted cards are allowed. You must use the card from the set and can't use reprints even going backwards. For example Ice Age contains Swords to Plowshares, you can't use a Revised one, or a crappy 4th one. You can't even use a gorgeous Beta one. Wrath of God is found only in Portal, you must use that one. If a card is in multiple legal sets you may use any, or mix and match to trigger your opponents.
Gold bordered "Championship" cards are permitted, given that they match a legal printing of the card and would be otherwise legal in the format. For example, you can use Survival of the Fittest, but you still can't use Birds of Paradise.
You may play basic lands from any of the promo sets in that time period, as well as those from Unglued.
Mana burn is on like donkey kong.
Wishes may retrieve cards from your sideboard or exile.
Graveyard order matters, a lot.
Other modern day rules, such as the London mulligan (the 7-7-7 mulligan), are in effect.
Observe List and Potential Changes
Here's a starter Scryfall search that you can use to check on whether various cards existed during this time period.
game:paper language:english border:black is:booster date>=fem date<=scg